The present invention relates to an image forming apparatus such as a printer device, a facsimile device, a copier, and an image forming apparatus of an MFP (Multi Function Product) combining these devices having a function of overlapping a specific pattern on a document or image data. The present invention further relates to an image forming system including the image forming apparatus, and a method of forming an image.
In a conventional office system, image information of a seal of an acknowledger is stored in a memory in advance. When various documents are issued, a mark is printed on a document at a specific position for acknowledging the seal. The mark is read through an optical device to determine that the seal can be printed, so that the image information of the seal is printed (refer to Patent Reference).    Patent Reference: Japanese Patent Publication No. 3-9874
In the conventional system, the mark, i.e., the simple acknowledgment information, is printed on the document at a specific position for acknowledging the seal, so that the image information of the seal is printed. However, it is relatively easy to fabricate the mark. Accordingly, anyone is able to print the seal, thereby causing security problem.
In view of the problems described above, an object of the present invention is to provide an image forming apparatus, in which it is possible to solve the problems in the conventional system.
Further objects and advantages of the invention will be apparent from the following description of the invention.